IUPAC Name, Structure and Formula of Straight Chain Alkanediols Chemistry Tutorial

Key Concepts

• Straight chain alkanediols are organic molecules containing only carbon (C), hydrogen (H) and oxygen (O) atoms.
• Alkanediols belong to the group of organic compounds known as alcohols.
• Alcohols are hydroxy compounds, they contain an OH, hydroxy (or hydroxyl)⁽¹⁾, functional group.
• A straight-chain alkanediol consists of a chain of 1 or more carbon atoms joined to each other by single covalent bonds, with two OH functional groups attached to either the same carbon atom in the chain, or, to two different carbon atoms in the chain.
• Note that an alkanol contains only ONE hydroxyl, OH, functional group

  while an alkanediol contains TWO hydroxyl, OH, functional groups

• The systematic IUPAC name⁽²⁾ of an alkane-n,n-diol is made up of three parts:

  (i) a prefix or stem

  (the name of the parent hydrocarbon (the alkane chain) alkane)

  (ii) an infix

  (two numbers which tell us the location of each of the OH functional groups, -n,n-)

  Note that the two numbers are separated by a comma

  Note that each number of the infix is separated from a letter by a hyphen

  (iii) a suffix

  (last part of the name, diol)

• The suffix when naming a straight-chain alkanediol is always "diol"
• The prefix or stem is dependent on the number of carbon atoms in the longest chain of carbon atoms (the parent hydrocarbon, or parent alkane):

  Number of carbon atoms:	1	2	3	4	5	6	7	8	9	10
  Prefix:	meth	eth	prop	but	pent	hex	hept	oct	non	dec

• The general molecular formula for a straight-chain alkanediol is C_nH_2n+2O₂

  where n = number of carbon atoms in the carbon chain

Please do not block ads on this website.
No ads = no money for us = no free stuff for you!

Steps for IUPAC Naming of Straight Chain Alkanediols

• The systematic IUPAC name of an alkane-n,n-diol is made up of three parts:

  (i) a prefix or stem (first part of the name, the name of the parent alkane) : alkane

  (ii) an infix (two numbers indicating the location of each of the OH functional groups) : -n,n-

  (iii) a suffix (last part of the name indicating the presence of the TWO OH functional groups) : diol

• The name of a straight chain alkanediol always ends in the suffix diol
• The first part of the name of a straight chain alkanol, its prefix or stem, is determined by the number of carbon atoms in the parent alkane chain:

  Number of carbon atoms:	1	2	3	4	5	6	7	8	9	10
  Prefix:	methane	ethane	propane	butane	pentane	hexane	heptane	octane	nonane	decane

Step 1: Identify the longest carbon chain containing both the OH (hydroxy or hydroxyl) functional groups.

Step 2: Determine the prefix for the name of the alkanediol based on the number of carbon atoms in the chain.

Step 3: Number each carbon atom along the longest carbon chain so that the carbon atoms bonded to the OH (hydroxy or hydroxyl) functional groups have the lowest possible numbers.

For a straight chain alkanediol this means the first number will be the lowest possible.

Step 4: Determine the infix for the name of the alkanediol based on the location of the OH (hydroxy or hydroxyl) functional groups.

Note that the infix may not be required if the longest carbon chain contains only one carbon atom.

Write the infix with the lowest number first followed by a comma then followed by the larger number

Step 5: Determine the suffix for the name of the alkanediol.

All straight chain alkanediols will end in "diol".

Step 6: Write the name for the alkanediol in the form of prefix-infix-suffix

Worked Example of IUPAC Name of Straight Chain Alkanediols: 1 Carbon Atom

Name the straight chain alkanediol shown below using systematic IUPAC nomenclature rules:

Step 1: Identify the longest carbon chain containing both the OH (hydroxy or hydroxyl) functional groups.

Step 2: Determine the prefix for the name of the alkanol based on the number of carbon atoms in the chain.

(The name of the parent alkane)

Longest carbon chain has 1 carbon atom.

Parent hydrocarbon is methane.

Prefix is methane

Step 3: Number each carbon atom along the longest carbon chain so that the carbon atom bonded to the OH (hydroxy or hydroxyl) functional groups have the lowest possible numbers.

Step 4: Determine the infix for the name of the alkanediol based on the location of both of the OH (hydroxy or hydroxyl) functional groups.

Note the infix is not required if the longest carbon chain contains only one carbon atoms.

This alkanediol has only 1 carbon atom so no infix is required.

Step 5: Determine the suffix for the name of the alkanediol.

All straight chain alkanediols will end in "diol".

Suffix is diol

Step 6: Write the name for the alkanediol in the form of prefix-infix-suffix

Systematic IUPAC name is methanediol

Other names: 1,1-methanediol or methane-1,1-diol

Worked Example of IUPAC Naming of Straight Chain Alkanediols: 2 Carbon Atom Chain

Name the straight chain alkanediol shown below:

Step 1: Identify the longest carbon chain containing both the OH (hydroxy or hydroxyl) functional groups.

Step 2: Determine the prefix for the name of the alkanediol based on the number of carbon atoms in the chain.

Longest carbon chain has 2 carbon atoms.

Parent hydrocarbon is ethane.

Prefix is ethane

Step 3: Number each carbon atom along the longest carbon chain so that the carbon atoms bonded to the OH (hydroxy or hydroxyl) functional groups have the lowest possible numbers.

Step 4: Determine the infix for the name of the alkanediol based on the location of both of the OH (hydroxy or hydroxyl) functional groups.

Note that the infix is not required if the longest carbon chain contains only one carbon atom.

Both OH groups are attached to carbon 1

infix is -1,1-

Step 5: Determine the suffix for the name of the alkanediol.

All straight chain alkanediols will end in "diol".

Suffix is diol

Step 6: Write the name for the alkanediol in the form of prefix-infix-suffix

Systematic IUPAC name is ethane-1,1-diol

Other names: 1,1-ethanediol

Worked Example of IUPAC Name of Straight-Chain Alkanediols: 3 Carbon Atom Chain

Name the straight chain alkanediol shown below using systematic IUPAC nomenclature rules:

Step 1: Identify the longest carbon chain containing both of the OH (hydroxy or hydroxyl) functional groups.

Step 2: Determine the prefix for the name of the alkanol based on the number of carbon atoms in the chain.

(The name of the parent alkane)

Longest carbon chain has 3 carbon atoms.

Parent hydrocarbon is propane.

Prefix is propane

Step 3: Number each carbon atom along the longest carbon chain so that the carbon atoms bonded to the OH (hydroxy or hydroxyl) functional groups have the lowest possible numbers.

Step 4: Determine the infix for the name of the alkanediol based on the location of both of the OH (hydroxy or hydroxyl) functional groups.

Note the infix is not required if the longest carbon chain contains only one carbon atom.

Note that the infix is written such that the smaller number comes before the larger number, and a comma separates the two numbers from each other.

In this molecule, one OH group is attached to the first carbon atom in the chain, C¹, and the other OH group is attached to the second carbon atom in the chain, C², so the infix is -1,2-

Step 5: Determine the suffix for the name of the alkanediol.

All straight chain alkanediols will end in "diol".

Suffix is diol

Step 6: Write the name for the alkanediol in the form of prefix-infix-suffix

Systematic IUPAC name is propane-1,2-diol

Other names: 1,2-propanediol

Steps for Drawing the Structure⁽³⁾ of Straight Chain Alkanediols

Step 1: Break the systematic IUPAC name of the alkane-n,n-diol into its three parts:

Note that the infix may be absent if the parent alkane chain contains only 1 carbon atom.

Step 2: Determine the number of carbon atoms in the longest alkane carbon chain using the prefix.

Step 3: Draw a chain of carbon atoms of the required length using dashes to represent a single covalent bond between each pair of carbon atoms.

Step 4: Draw dashes around each carbon atom in the chain such that each carbon atom makes 4 bonds.

Step 5: Number the carbon atoms in the chain from left to right.

Step 6: Determine the location of each of the OH (hydroxy or hydroxyl) functional groups using the infix.

We know there are two OH functional groups because the molecule's name has the suffix diol.

Step 7: Draw each OH group at the end of a dash on the carbon with the same number as the infix.

Step 8: Complete the structure by placing a hydrogen atom (H) at the end of all the vacant dashes.

Worked Example of Drawing the Structure of a Straight-Chain Alkanediol

Draw a structure for the straight chain alkanediol ethane-1,2-diol (also known as ethylene glycol)

Step 1: Break the systematic IUPAC name of the alkane-n,n-diol into its three parts:

Note that the infix may be absent if the parent alkane chain contains only 1 carbon atom.

Step 2: Determine the number of carbon atoms in the longest alkane carbon chain using the prefix.

Prefix is ethane

ethane indicates the parent alkane chain contains 2 carbon atoms with single covalent bonds between each carbon atom in the chain.

Step 3: Draw a chain of carbon atoms of the required length using dashes to represent a single covalent bond between each pair of carbon atoms.

Step 4: Draw dashes around each carbon atom in the chain such that each carbon atom makes 4 bonds.

Step 5: Number the carbon atoms in the chain from left to right.

Step 6: Determine the location of each of the OH (hydroxy or hydroxyl) functional groups using the infix.

We know there are two OH functional groups because the molecule's name has the suffix diol.

infix is -1,2- therefore one OH group is attached to the first carbon atom in the ethane chain, and the second OH functional group is attached to the second carbon atom in the chain.

Step 7: Draw the OH groups at the end of a dash on the carbon with the same number as the infix.

infix is -1,2- therefore one OH group is attached to the first carbon atom, and the other OH group is attached to the second atom in the ethane chain.

Step 8: Complete the structure by placing a hydrogen atom (H) at the end of all the vacant dashes.

Steps for Writing the Molecular Formula of Straight Chain Alkanediols

A molecular formula tells us the number of atoms of each element present in a molecule of the compound.

For a straight-chain alkanediol, only three elements are present, carbon (C), hydrogen (H) and oxygen (O).

When writing the molecular formula of an alkanediol, the number of carbon atoms is written before the number of hydrogen atoms which is written before the number of oxygen atoms, that is, C is written before H which is written before O⁽⁴⁾:

C_xH_yO₂

Step 1: Draw the structure of the alkane-n,n-diol molecule.

Step 2: Write a skeleton molecular formula using the symbols for carbon (C), hydrogen (H) and oxygen (O).

C H O

Step 3: Count the number of carbon atoms in the alkanediol molecule.

Step 4: Write the number of of carbon atoms into the skeleton molecular formula as a subscript number to the right of the symbol for carbon (C).

Step 5: Count the number of hydrogen atoms in the alkanediol molecule.

Step 6: Write the number of of hydrogen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for hydrogen (H).

Step 7: Count the number of oxygen atoms in the alkanediol molecule.

Step 8: Write the number of of oxygen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for oxygen (O).

Note: if only two hydroxy (or hydroxyl, OH) groups are present, the number of oxygen atoms is 2.

Step 9: Check that your completed molecular formula makes sense (C_nH_2n+2O₂)

Worked Example of Writing the Molecular Formula of a Straight-Chain Alkanediol

Write the molecular formula for butane-1,3-diol (1,3-butanediol).

Step 1: Draw the structure of the alkane-n,n-diol molecule.

Step 2: Write a skeleton molecular formula using the symbols for carbon (C), hydrogen (H) and oxygen (O).

C H O

Step 3: Count the number of carbon atoms in the alkanediol molecule.

Step 4: Write the number of of carbon atoms into the skeleton molecular formula as a subscript number to the right of the symbol for carbon (C).

C₄H O

Step 5: Count the number of hydrogen atoms in the alkanediol molecule.

Step 6: Write the number of of hydrogen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for hydrogen (H).

C₄H₁₀O

Step 7: Count the number of oxygen atoms in the alkanediol molecule:

Step 8: Write the number of of oxygen atoms into the skeleton molecular formula as a subscript number to the right of the symbol for oxygen (O).

Two oxygen atoms are present in this molecule, O₂

Molecular formula for butane-1,3-diol is C₄H₁₀O₂

Step 9: Check that your completed molecular formula makes sense (C_nH_2n+2O₂)

n = number of carbon atoms = 4

number of hydrogen atoms = 2 × n + 2 = 2 × 4 + 2 = 10

number of oxygen atoms = 2

Summay Table: Molecular Formula, Structure and IUPAC Name of Some Alkanediols